The production of rubber-like polymers has been investigated over the past years. Ring-opening metathesis polymerization of cyclopentene yields a linear polymer known by a common name of polypentenamer having a structure similar to that of poly-1,4-pentadiene, but having slightly lower double bond density in the main chain. The polymer has properties to enable the use as a general-purpose rubber, as can be supposed from its structure.
In order to obtain a rubber having characteristic features, a metathesis polymer of norbornene, which has high ring strain and is easily polymerizable by metathesis polymerization, has been industrially produced. Since the glass transition point of poly(norbornene) is higher than normal room temperature and slightly lower than 40.degree. C., the polymer is not rubbery, but plastic at normal room temperature. However, transition to a rubbery state takes place by slight heating of the polymer and the use of the polymer as a shape-memory polymer has been suggested to take advantage of the transition property. On the other hand, to make the polymer useful as a rubber, a rubber processing oil is added to the polymer to lower the apparent glass transition point and the polymer is crosslinked by conventional vulcanization to obtain a rubber. The rubber produced by the above process is used in various applications as a rubber having low resilience.
On the other hand, a process has been proposed to form a molded polymer article by using a low cost metathesis polymerizable cycloolefin having two metathesis polymerizable cycloolefin groups, for example dicyclopentadiene (DCPD), and carrying out the polymerization and molding of the cycloolefin in a mold (in one step) with a metathesis polymerization catalyst. More particularly, a process has been proposed to obtain a molded polymer article, taking advantage of the fact that a metathesis polymerization catalyst system is composed of two components, i.e. a catalyst component such as a tungsten chloride and an activator component such as an alkylaluminum. Two solutions each containing one of the above catalyst system components and monomer, are quickly mixed and transferred into a mold (for example, U.S. Pat. No. 4,400,340) where polymerization and shaping take place.
Such a process is attractive for producing a crosslinked molded polymer article because the molding can be carried out at a high speed simultaneously with polymerization, using a low-pressure, relatively inexpensive mold. The polydicyclopentadiene produced by this process is generally a plastic having a thermal deformation temperature of 90.degree. C. or higher.